在DiagrammeR包中创建图例

Question

我正在尝试为我的图表流程图创建图例。到目前为止，我已经创建了流程图，但是我不知道如何添加图例来解释我的编号。

library(DiagrammeR)


grViz("


digraph dot {

graph [layout = dot,
       rankdir = LR]

node [shape = square,
      style = filled,
      color = grey,
      fontname = Helvetica]


node [fillcolor = white] 
a [label = 'Location 1']



node [fillcolor = green]
b [label = 'Location 2']

node [fillcolor = orange]
c [label = 'Location 3']
d [label = 'Location 4']



edge [color = grey]
a -> {b} [label = '1,2']
b -> {c} [label = '1']
b -> {d} [label = '2']




}")

这就是我想要的：